'I have eaten' is the present perfect tense of the verb 'to eat', 'I had eaten' is the past perfect and 'I will have eaten' is the future perfect.
Ihave eaten是动词eat的现在完成时；Ihad eaten是过去完成时；Iwill have eaten是将来完成时。
We use the present perfect tense to tell how many times an action has happened till now.
我们用一般过去时谈论发生在过去的动作和事情。
We use the present perfect tense to talk about something that happened at an indefinite time in the past.
我们使用现在完成时谈论发生在过去某个不确定的时间的事情。
We use the present perfect tense to talk about an action that started in the past and continues to the present.
我们用一般过去时谈论发生在过去的动作和事情。
We use the present perfect tense to talk about things that started in the past and still have some connection with the present.
我们用现在完成时来谈论在过去开始并且仍与现在有联系的事情。
In English learning, it is difficult for learners to master the tense, especially the past tense and the present perfect tense.
英语学习中，时态的学习和运用对学习者尤其中低水平学习者来说是一个困难之处。
They appear more excited when we talk about university life in the United States than when we discuss the correct usage of the present perfect tense.
与讨论如何正确使用现在完成时相比，当我们谈起美国大学的生活时，他们显得更为兴奋。
Right now, your problems are probably more basic: mistakes in pronunciation, small vocabulary, grammar problems with the present perfect tense and conditional structures.
现在，你的问题大概更基础：发音上的错误，小词汇量，现在完成时的和条件句的结构的语法问题。
When you ask about something that started in the past but continues to the present time, you use the Present Perfect tense, e.g.: I’ve been there for 5 years / I’ve been there for 5 years.
当你谈论在过去开始但是一直持续到现在的某事时，用现在完成时态，例如：I’vebeentherefor5years/我在那里已经5年了。
So you learn the past tense and then two or three weeks later, oh now you are learning the present perfect, and then a few weeks later, you are learning the future, that's crazy.
你学习了过去时，然后两到三周后你开始学习现在完成时，几周以后你又开始学习将来时，这简直太疯狂了。
As one of the most important and confusing grammatical tenses in high-school English, present perfect tense brings about much perplexity to both teachers and students.
现在完成时态是中学英语语法中的重点和难点，经常给师生带来困惑。
To grasp the usage of the tenses, including the present, past, future tense and continue, perfect tense.
掌握现在时，过去时，未来时， 进行时， 完成时的各种用法。
In this case, the past or present perfect tense should be used according to the grammatical rules of common English.
若按普通英语的动词时态规则，就得用一般过去时或现在完成时。
To grasp "the Present Perfect" and the Irregular verbs' past tense &past participle tense.
中文意思：掌握现在完成时态以及不规则动词的过去时态和过去分词…
The second function of the present perfect continuous tense is to talk about an action that started in the past and it is still happening.
第二种：谈论一个起始于过去，但是现在仍在发生的动作。
The second function of the present perfect continuous tense is to talk about an action that started in the past and it is still happening.
第二种：谈论一个起始于过去，但是现在仍在发生的动作。
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